web/web_widget_url_listview/data/assets_backend.xml

<?xml version="1.0" encoding="UTF-8"?>                                         
<openerp>                                                                      
    <data>                                                                     
        <template
            id="assets_backend"
            name="web_widget_url_listview assets"
            inherit_id="web.assets_backend">
            <xpath expr="." position="inside">                                 
                <script
                    type="text/javascript"
                    src="/web_widget_url_listview/static/src/js/web_list_url_widget.js">
                </script>
            </xpath>                                                           
        </template>                                                            
    </data>                                                                    
</openerp>